Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $240.81   9.751%   $264.2914   $264.29   $264.30   $264.30  
  Purchase #2 $30.94   8.864%   $33.6825   $33.68   $33.70   $33.70  
  Purchase #3 $108.38   11.569%   $120.9185   $120.92   $120.90   $120.90  
  Purchase #4 $77.27   13.371%   $87.6018   $87.60   $87.60   $87.60  
  Purchase #5 $176.98   11.649%   $197.5964   $197.60   $197.60   $197.60  
  Purchase #6 $237.94   9.272%   $260.0018   $260.00   $260.00   $260.00  
  Purchase #7 $148.83   4.622%   $155.7089   $155.71   $155.70   $155.70  
  7 purchase totals = $1,021.15       $1,119.8013   $1,119.80   $1,119.80   $1,119.80